The present invention relates to a pneumatic tire provided in the sidewall portion with an embossed mark, more particularly to a structure of the embossed mark capable of preventing occurrence of cracks.
In general, a pneumatic tire is as shown in FIG. 4, provided in the sidewall portion (b1) with embossed marks (a) in order to indicate various information on the tire and often for decorative purposes.
In recent years, on the other hand, in the field of passenger car tires, low profile pneumatic tires having very low aspect ratios such as 40% and 30% have been placed on the market.
In the case of pneumatic tires having relatively high aspect ratios, during running, the tire sidewall portions are repeatedly subjected to relatively large bending deformation in the ground contacting patch of the tire. Therefore, the embossed marks made from the sidewall rubber composition can endure such bending deformation.
In contrast, in the case of very low aspect ratio tires, the tire section height is very low and the radial dimension of the sidewall portions is very small. Accordingly, the sidewall portions are very hard to make bending deformation, and the sidewall portions in the ground contacting patch are subjected to large compressive deformation.
On the other hand, the embossed marks are protrude from the outer surface (b) of the tire sidewall portion (b1), therefore, the embossed marks are not subjected to compressive deformation, and a large shear stress occurs on the inside corner (f) between the outer surface (b) of the tire sidewall portion (b1) and the side surface (d) of the embossed mark (a) especially circumferentially extending side surface (g).
As a result, the very low aspect ratio tires suffer from cracks occurring at the inside corners of embossed marks such as the alphanumeric tire code which can not be omitted.
If the amount of protruding of the embossed mark is large like a block or rib formed in the tread portion, then concentration of the shear stress may be avoid by rounding the inside corner. But, the amount of protruding of the embossed mark is very small, therefore, if effectively rounded with a relatively large radius of curvature, then the border of the embossed mark becomes vague and the visibility and attractiveness of the embossed mark are greatly deteriorated. Thus, this technique can not be employed.